a.
1.
Stable, fixed, immutable, unvaried, invariable, unchanging, permanent, perpetual.
2.
Uniform, regular, stated, certain.
3.
Resolute, firm, steady, steadfast, stanch, determined, unshaken, unwavering.
4.
Persevering, assiduous, unremitting.
5.
Incessant, uninterrupted, unbroken, perpetual, continuous, continual.
6.
Faithful, true, trusty, loyal, devoted.